Venerable Bhante Vimalaramsi talks about the 7 Factors of Enlightenment. He also addresses what he considers a misunderstanding by scholars of how high the Metta Meditation will lead the meditator. You can attain the 4th jhana through Metta, 5th with Compassion, 6th Sympathetic Joy and 7th Nothingness.

Some texts note that you can only get to the 3rd Jhāna with Metta, however Bhante Vimalaramsi gives the Sutta reference for the proof that, in fact, the Suttas say that the practice of the Brahma Viharas leads you all the way up to the 7th Jhāna and from there he explains how you attain Nibbana.